Cognitive Medium Access: Exploration, Exploitation and Competition

TL;DR

This paper models cognitive medium access as a multi-armed bandit problem, deriving optimal strategies for single and multiple users to efficiently explore and exploit spectrum opportunities without prior traffic knowledge.

Contribution

It introduces a Bayesian approach to derive optimal and low-complexity medium access strategies for both single and multiple cognitive users, extending to multi-channel sensing scenarios.

Findings

Optimal Bayesian strategy derived for single-user case.

Low complexity asymptotically optimal strategies developed.

Protocols effectively balance exploration and exploitation in competitive environments.

Abstract

This paper establishes the equivalence between cognitive medium access and the competitive multi-armed bandit problem. First, the scenario in which a single cognitive user wishes to opportunistically exploit the availability of empty frequency bands in the spectrum with multiple bands is considered. In this scenario, the availability probability of each channel is unknown to the cognitive user a priori. Hence efficient medium access strategies must strike a balance between exploring the availability of other free channels and exploiting the opportunities identified thus far. By adopting a Bayesian approach for this classical bandit problem, the optimal medium access strategy is derived and its underlying recursive structure is illustrated via examples. To avoid the prohibitive computational complexity of the optimal strategy, a low complexity asymptotically optimal strategy is developed. The proposed strategy does not require any prior statistical knowledge about the traffic pattern on the different channels. Next, the multi-cognitive user scenario is considered and low complexity medium access protocols, which strike the optimal balance between exploration and exploitation in such competitive environments, are developed. Finally, this formalism is extended to the case in which each cognitive user is capable of sensing and using multiple channels simultaneously.